Timing, Emmissions, Carbs

[Jarvo2]

Last year I rebuilt my carbs with a ZTherepy kit and couldn't be happier with the results, very high quality product and informative video. My vacuum gauge is reading a steady 19 at idle and the car performs well and my plugs look good (not rich nor lean).

The main issue I've had is that when I adjust the SU's to allow for the pin lift test to work (slight RPM increase then return to normal), I need to richen the mixture so much I get a big cloud of black smoke out the exhaust and the vacuum gauge lowers to approximately 12-13 and the engine runs rough.

I recently removed my emissions gear (smog pump, dashpots, etc.) and closed off all of the vacuum ports to ensure I don't have any unmetered air going into the system.

My ignition timing is still set at 7 degrees BTDC as per the FSM. Now that I don't have the emissions equipment, should I increase the timing upto 15-17 degrees BTDC to account for the change in the engine as per the FSM? Will this improve the performance of the engine at all and allow me to properly set the lean/rich mixture??

I have recently adjusted my valves and have checked for vacuum leaks and I'm also running a Pertronix ignition. Any thoughts you may have would be appreciated!! Thanks.

- Dave

[Walter Moore]

If you have the OEM 72 distributor, even with the Pertronix kit installed, you have to stay at the stock static timing. That dizzy has a very large, 24 degree, centrifugal advance and if you advance the static timing beyond the standard setting you will have spark knock and potential engine damage.

[Jarvo2]

Thanks for the insight, Walter. I agree completely with you regarding the total amount of advance. So based on this, is it safe to assume that the non-emission L24's had a different distributor with a less aggressive centrifugal advance?

This then leads me to the ultimate question of carb-tuning. Should I be happy with the performance I have even though the pin-lift test doesn't work? Based on lifting the piston 1/16" the engine boggs down which leads me to think its running lean, although everything else is pointing to its tuned correctly. I recently picked up a colourtune which I hope can help me see what's going on in the combustion chamber.

[Stanley]

MSA used to sell a "240Z European distributor" for $200. Quote from their catalog: "As supplied by Datsun on 240Z's sold in Europe. Quicker advance curve."

I got one - it gave better performance and solved my cold start problem, but that was compared to the '73 dual-point distributor. Also it wasn't worn out. Don't think MSA has them anymore but I see new ones all the time advertised in Japanese magazines like Nostalgic Hero, one of the sites that import JDM stuff could probably get you one.

[Jarvo2]

Thanks for the info, Stanley.

I have two distributors, both with the same # on the first line, but different second lines. Can anyone tell me the specs on either of these? They both perform well, I'm guessing they just have different advance curves.

D612-53

112b

D612-53

205

[Jarvo2]

I think I'm going to try to pop my SM needles out and reinstall the N58's which came with the car when I purchased it.